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 ###Instrução: Quais dias o greenock morton está vago?
 ###Tabelas: CREATE TABLE female_names (female_names_id AUTO_INCREMENT PRIMARY KEY, Region (year) VARCHAR, No. 1 VARCHAR, No. 2 VARCHAR, No. 3 VARCHAR, No. 4 VARCHAR, No. 5 VARCHAR, No. 6 VARCHAR, No. 7 VARCHAR, No. 8 VARCHAR, No. 9 VARCHAR, No. 10 VARCHAR) CREATE TABLE managerial_changes (managerial_changes_id AUTO_INCREMENT PRIMARY KEY, Team VARCHAR, Outgoing manager VARCHAR, Manner of departure VARCHAR, Date of vacancy VARCHAR, Replaced by VARCHAR, Date of appointment VARCHAR) CREATE TABLE singles_7_titles_-_8_runner-ups (singles_7_titles_-_8_runner-ups_id AUTO_INCREMENT PRIMARY KEY, Outcome VARCHAR, Date VARCHAR, Tournament VARCHAR, Surface VARCHAR, Opponent VARCHAR, Score VARCHAR) CREATE TABLE pga_tour_wins_5 (pga_tour_wins_5_id AUTO_INCREMENT PRIMARY KEY, Date VARCHAR, Tournament VARCHAR, Winning score VARCHAR, Margin of victory VARCHAR, Runner(s)-up VARCHAR) CREATE TABLE highest_scoring_grand_finals (highest_scoring_grand_finals_id AUTO_INCREMENT PRIMARY KEY, Total Points INT, Score VARCHAR, Premiers VARCHAR, Runners Up VARCHAR, Details VARCHAR)  
SELECT Date of vacancy FROM managerial_changes WHERE Team = Greenock Morton